Lockout switch



vFoal). 12 1924.

T. E. BARNUM ELECTRIC SWITCH Original Filed Nov. 13, 1918 3 Sheets-Sheet 1 Feb. 12 1924. v 1,483,407

T. E. BARNUM ELECTRIC SWITCH Original Filed Nov. 13 1913 s Sheets-shut -z 2' o I 611 361195 5 6 .l

I flaw/ZZZ ww; 5&17362/170 Feb. 12 1924. 1,483,407

T. E. BARNUM ELECTRIC swn'cu Original Filed Nov- 13 1 3 Sheets-Sheet 3 lllllL IIIIIII o ff;

5;.- a amm n Patented Feb 12, 1924.

UNITED STATES PATENT OFFICE.

THOMAS E. BABNUM, F MILWAUKEE, WISCONSIN, ASSIGNOR TO THE CUTLER-HAM- MER MFG. 00., 0F MILWAUKEE, WISCONSIN, A CORPORATION OF WISCONSIN.

nooxou'r swrrcn.

Continuation of application Serial No. 800,700, filed November 13, 1913. This application filed February 5, 1915, Serial No. 6,247. Renewed December 22, 1920. Serial No. 432,600.

To all whom it may concern Be it known that I, THOMAS E. BARNUM, a citizen of the United States, residing at Milwaukee, in the county of Milwaukee and State of Wisconsin, have invented new and useful Improvements in Lockout Switches, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawing, forming a part of this specification.

This invention relates to an electromagnetically operated switch. I

It will be explained as ap lied to a switch in Which two separate an independcut electromagnets, one a holding magnet and the other an actuatin opposition upon a pivote beam or other means which control the movable switch contact.

Such a switch is disclosed in United States Letters Patent No. 1,151,550, August 24, 1915, issued to George H. Whittingham.

It is particularly adapted to control resistance which is employed to start an electric motor, but it may be applied to other purposes.

The beam is biased to an initial position to open the switch and movable to a final position to close the switch. I

The two electromagnets have the windings thereof connected in series with each other and the motor armature so that both windings are subjected to the same variation in current as the motor armature.

The, separate and independent magnets exert relatively varying pulls in opposition to each other under similar variations in current so that the holding magnet predominates when the current is abnormal or 4o above a predetermined value and the actuating magnet predominates when the current is normal or at or below such predetermined value.

As a result, if the current rises above the predetermined value at which the beam is to be actuated to close the switch, as occurs when the motor armature circuit is first closed or resistance is IGIIIOVBd lLhGH-B- from, the holding magnet retains the beam in its initial position and keeps the switch open until the motor armature speed inmagnet, act in high pull to seal the switch contacts when the beam is moved to its final position to close the switch.

To produce a lookout switch which is efficient and which may be readily and economically manufactured.

In accordance with this invention, the actuating magnet has a comparatively closed magnetic circuit of relatively low reluctance so that sufiicient eddy currents will be created to produce a high counter magnetomotive force, under a sudden increase in cur rent, to oppose the rise in flux.

The magnetic circuit may further be provided with a shunt or by-pam in parallel to the armature. This shunt or by-pass ini tially diverts flux from the armature and increases the flux in the'magnet pole pieces, thereby causing a further delay in the pull upon the armature due to the flux diverted therefrom and the increased eddy currents.

When the armature is attracted and approaches the magnet pole pieces, the flux, which previously passed through the shunt, traverses the armature and thus a materially increased pull is created thereon.

This application is a continuation of application Serial No. 800,700, filed November 13, 1913.

An-embodiment of the invention is illustrated in the accompanying drawings, in which the views are as follows:

Fig. 1 is a side elevation of the switch.

Fig. 2 is a vertical section, the switch being open.

' Fig. 3 is a vertical section, the switch being closed.

Fig. 4 shows two pull curves when the switch is closed, one being of the closing magnet with the shunt and the other being 1 of a similar magnet without the shunt.

Fig. 5 is a diagram comparing the pull characteristics of the actuating or closing magnet and the holding or lockout magnet.

Fig. 6 is a diagram showing the flux in the magnetic circuit of the closing magnet with the shunt and the flux in the magnetic circuit of a similar magnet without the shunt.

Fig. 7 is a diagrammatic view of a controller employing the lockout switch set forth herein.

The switch has a beam 1 and two separate and independent electromagnets, an actuatin or closing magnet 2 and a holding or loc liout magnet 3.

The beam 1 is mounted upon a pivot 4, and carries a pivoted movable contact 5, which may engage a fixed contact 6. It is biased to an initial position, wherein the switch is open, contacts 5 and 6 being separated, and is-movable to a final position wherein the switch is closed. A stop 7 fixes the initial position in which the beam normally stands.

The actuating and holding magnets act upon the beam on opposite sides of its pivot. The pull of the actuating magnet tends to move the beam to close the switch and the pull of the holding magnet tends to retain the beam in its initial position and keep the switch open.

The actuating magnet has two pole pieces, an inner pole piece 8 and an outer pole piece .9, connected together at one end and separated at the other. The outer end of pole piece 9 is provided with a shunt 10, which, with a short air gap 11, forms a magnetic shunt or by-pass to the armature.

The actuating magnet has a comparatively closed magnetic circuit of relatively low reluctance. The shunt providesa by-pass in parallel to the armature so that, in initial position of the beam, a relatively large proportion of the flux in the actuating magnet is diverted from its armature and exerts no pull thereon. As the beam approaches its .final position the proportion of the flux diseparate and independent magnetic circuits so that the magnetic fluxes,and the pulls exerted thereby upon the beam, are independent ofieach other.

When the beam is in initial position and the switch 'is open the greater portion of the flux created by current passing through the Winding of the actuating ma net passes through outer pole piece 9 an shunt 10 across air gap 11 back to the inner pole piece. A smaller portion of the flux passes through outer pole piece 9, beam 1, andacross the longer air gap between the inner pole piece and the armature, back to the inner pole piece. The flux, passing through shunt 10 and across air gap 11, exerts no pull upon the beam, although this flux acts to magnetize theipole pieces. A smaller percentage of the ux, passing across the air gap between the armature and inner le piece, exerts a pull upon the beam tendi iig to move it from its initial position and close the switch.

The actuating magnet, having a comparatively closed magnetic circuit, will increase the'flux therein for increases in current at low values comparatively greater than will the holding magnet which has a comparatively open magnetic circuit. On the other hand, at comparatively high current values the flux created in the actuating magnet will not increase as greatly for increases in current as will the fiux in. the holding magnet. The pull of the magnets, which depends upon the flux. therein, consequently varies by different ratios when the current changes occur at higher and lower values.

' Fig. 5 shows curves representing the ull characteristics of the actuating and 1101 ing magnets for a given range of current values. Curve C shows how the pull of the actuating magnet varies with the current and curve H illustrates how the pull of the :holding magnet varies over the same current range. At the lower current values the pull of the actuating magnet increases-t0 a greater extent, for a given current increase, than does the pull of the holding magnet. For relatively higher current values the reverse condition obtains.

In practice the current rises suddenly when the armature circuit is closed or resistance is removed therefrom. As the speed of the motor and consequently the counter e1ectromotive force rises comparatively slowly, the armature current subsides slowly to normal. The switch, in order to protect the motor a ainst excessive current, remains open, to eep resistanceein circuit, when the current rises suddenly above the critical value but closes to exclude resistance when The comparatively large conducting mass of the outer pole piece causesjthe production of comparatively heavy eddy currents in the actuating magnet so that the rise of its fiux and consequently the increase in its'pull on the beam lags ehind the rise o f the flux and pull cf the holding magnet. Thus the pull of the actuating magnet does not predominate to close the switch as the current suddenly rises above the critical value.

As the speed of the motor increases, the

current slowly subsides to the critical value. The comparatively slow change in the current creates comparatively small eddy cur rents and there is consequently little opposition to the decrease in the flux in either magnet. The pull characteristic of the actuating magnet is thus changed but slightly if at; all and at the critical current the pull of the actuating magnet predominates and moves the beam from its initial position to its final position to close the switch.

The outer pole piece, in addition to assisting in the magnetization and the alteration of the pull characteristic of the actuating magnet cooperates. with the, armature thereof to augment the pull produced by the actuating magnet as the beam approaches the magnet and after it' reaches its final position.

\Vhen the beam is in its initial position a comparatively large proportion of the flux through the inner pole piece is shunted or by-passed from the armature, and accordingly produces no pull upon the beam. When the beam approaches its final position and the pulling air gap decreases in length, a smaller amount of the fiuxpasses through the shunt or bypass including the outer pole piece and air gap 11 and more of the flux passes into beam 1 and across the pulling air gap. Thus the pull of the actuating magnet increases materially as the beam approaches its final position. \Vhcn the beam reaches its final position, the pulling air gap is completely or almost completely closed and practically all of the 'fiux passes into the armature and is efiective to maintain the beam in final position with the switch closed.

The effect of the by-pass upon the pull and flux of the actuating magnet is graphically shown by the curves of Figs. 4

and 6. v

In Fig. 4 the pull in pound-inches is plotted as ordinates and the current in the winding as abscissae. Curve D represents the sealing pull of an actuating magnet having a by-pass and curve B represents the sealing pull of an actuating magnet without the bypass. The curves show that the sealing pull is greater for each value of the current when .a by-pass is employed and that the pull becomes relatively greater as the current value is increased.

In Fig. 6 the flux in the core of the actuating magnet with and without a by-pass is plotted as ordinates and the current in the winding is plotted as abscissae. flux, for every current value, is higher when the by-pass or comparatively closed magnetic circuit is used than when no by-pass or a comparatively open magnetic circuit is used. The curves show how the magnetization of a closed circuit magnet increases more rapidly than the magnetization of an open circuit magnet.

Fig. 7 diagrammatically illustrates the application of the switch set forth herein to control the starting resistance for an electric motor.

The motor has an armatuie 14 and a shunt field 15 which are connected to positive line 16 and negative line 17.

The armature current is regulated by starting resistances 18, 19 and 20.

These resistances are controlled by switches 21, 22 and 23, respectively.

In order to start the motor, the switch. 24 is closed by closing the switch 25.

Current then fiowsfrom the conductor 16 through switch 24, magnets 2 and 3 of switch 21, resistances 18. 19 and 20, armature 14, to negative line 17.,

As the armature is at rest, the current may become abnormal. and then the switch 21 is held open by its holding magnet 3.

lVhen the armature accelerates sulficiently to make the current subside to a critical value. the switch 21 is closed by its actuating magnet 2.

The resistance 18 is then short-circuited and the switch 22 has the windings of its magnets connected in circuit.

If the current becomes abnormal, due to the resistance 18 being removed from circuit, the switch 22 will be held open by its holding magnet until the motor armature. accelerates sufi'lciently to reduce the current to a critical Value.

When the switch 22 closes, it short-cir cuits the resistance 19. and the switch 23 has the windings of its magnets connected in circuit.

WVhen the switch 23 finally closes, it removes resistance 20 from circuit.

Of course, various modifications may be made in the switch set forth herein and the application thereof without in any way departing from the invention.

Having shown and described an embodiment of my invention, what I claim as new and desire to secure by Letters Patent, 1s,-

1. An electromagnetic appliance having a pivoted member normally biased to one position and movable to another position. a pair of electromagnets acting on said memher in opposite directions. said electromagnet's having independent magnetic circuits and different pull characteristics when sub- The member to another position undercurrent 7 jected to the same change in currentso that one predominates under current above a predetermined value and the other predominates under current below a predetermined value, and means for causing the pull of the second electromagnet to increase less rapidly than the pull of the first electrom'agnet under sudden rises of current.

2. An electromagnetic switch having a pivoted member normally biased in one position, two electromagnets acting in opposite directions upon said member and having independent magnetic circuits and dift'erent pull characteristics when subjected to similar current conditions so that one electroinagnet predominates to hold said memlier in its initial position under current above a predetermined value and the other electromagnet predon'iinates to move said below a predetermined value, and means to delaythe increase in pull of the second electromagnet under a sudden rise of current.

3. An electromagnetic switch having a pivoted member normally biased in one position and movable to anotherposition, two magnetically independent electromagnets subject to the same current conditions and acting on said member in opposite directions one to assist in holding said member in its initial position and the other for moving said member, said electromagnets having difl'erent pull characteristics whereby the one assisting in holding said member in its initial position predominates under current above a predetermned value while the other predominates under current below a predetermined value, and means for delaying the predominance of the second electromagnet when subjected to suddenly increasing current.

'4. An electromagnetic switch having a movable member pivoted intermediate its *ends, a pair of electromagnets acting on said member 1n opposite directions, said electromagnets having independent magnetic cir-'- cuits and different .pull characteristics when subjected to similar current variations so that onepredominates under current of abnormal value and the other predominates under current below an abnormal value, and means for delaying the increase in pull of the'second electromagnet' when the current changes suddenly.

5. An electromagnetic switch having a -pivoted member movable to two positions, a

pair of electromagnets exerting opposing pulls upon said member, said electromagnets having independent magnetic circuits and different pull characteristics so that when subjected to the same current conditions the pull of one electromagnet predominates undercurrent above a predetermined value and the pull of the other predominates under current below a predetermined value, and V under means for retarding the increase in pull of the second electromagnet under sudden, rises of current below the predetermined value.

6. An electromagnetic switch having a member pivoted intermediate its ends and normally biased in one position, a holding elcctromagnet for assisting in retaining said member in its initial position, an actuating electromagnet acting in opposition to said holding electromagnet to move said member to another position, said electromagnets be ing subjected to the same current conditions but having independent magnetic circuits and exerting relatively varying pulls on said member under different current values so that the holding electromagnet predominates under current above a predetermined value and the actuating electromagnet"predominates under current below a predetermined value, and means for retarding the preponderance of the actuating electromagnet under sudden rises of current below the predetermined value.

7.- An electromagnetic switch having a pivoted member, two electromagnets acting upon said member to attract it in opposite directions, said electromagnets having independent magnetic circuits and different pull characteristics so that one predominates under current above a predetermined value and the other predominates under current below a predetermined value, and means for causing a part of the fluxof one electromagnet to be diverted from attracting said member until after said member approaches said electromagnet.

8. An electromagnetic switch having a pivoted member initially biased in one position and movable to another osition, two electromagnets actingin opposite directions uponsaid member and having independent magnetic-circuits and different pull characteristics when subjected to similar current conditions so that one predominates current above a. predetermined value and the other predominates under current below a predetermined value; and means for decreasing the flux of the second electromagnet acting upon said mem' her in its initial position.

9. An electromagnetic switch having a pivotedmember, two electromagnets acting upon said member to attract it in opposite directions, said electromagnets having independent magnetic circuits and different pull characteristics so that one predominates undercurrent above a predetermined value and the other predominates under current below a predetermined value, and means .for diverting a part of the flux of the second electromagnet from attracting said member before said member is moved, such part of the flux diminishing as said member approaches said electromagnet.

.10. An electromagnetic appliance comprising two separate and independent electromagnets one having a comparatively closed or low reluctance magnetic circuit and the other having a comparatively open or hi h'reluctance magnetic circuit, and a movaEle member attracted in opposite direc tions by said electromagnets.

11. An electromagnetic appliance comprising two separate and independent electromagnets one having a comparatively closed or low reluctance magnetic circuit and the other having a comparatively open or high reluctance magnetic circuit, and a movable member attracted in opposite directions by said electromagnets, the low reluctance magnet having a magnetic shunt including an air gap between its poles and in shunt with its armature.

12. An electromagnetic appliance having a movable member movable from one position to another, a relatively low reluctance or closedmagnetic circuit magnet'to move said member to one position, and a separate relatively high reluctance open magnetic circuit magnet to hold said member in the other position.

13. An electromagnetic appliance having a movable member movable from oneposition to another, a relatively low reluctance or closed magnetic circuit magnet to move said member to one position, and a separate relatively high reluctance open magnetic circuit magnet to hold said member in the other position, such magnets having different changes in pull under the same changes in current. a

14. An electromagnetic appliance having a member movable between two different positions, a relatively low reluctance or closed magnetic circuit magnet to attract said member in one direction, and a separate relatively high or open magnetic circuit magnet to attract said member in the opposite direction, the magnetic circuit being smaller and the ampere turns greater upon the first ma et than upon the second.

15. An e ectromagnetic appliance comprising two separate and independent electromagnets one having a comparatively closed or low reluctance magnetic circuit of relatively large cross-section and the other having a comparatively open or high reluctance magnetic circuit, and a movable member attracted in opposite directions by said electroniagnets, the low reluctance magnet having a magnetic shunt including an air gap between its poles and in shunt with its armature to provide a supplemental flux to increase the magnetization and decrease the initial pull upon thev armature.

16. An electromagnetic appliance having a movable member, and two separate and independent electromagnets acting in opposite directions upon said member, one having a relatively open or high reluctance magnetic circuit and the other having a relatively closed or low reluctance magnetic circuit, the second magnet having a magnetic shunt with an air gap between its poles and in shunt with its armature to provide .an additional flux to augment the normal increase in pull upon the armature as it approaches such magnet.

17 An electromagnetic appliance comprising a movable member provided with an armature, a low reluctance or closed magnetic circuit magnet to attract said armature, said magnet having a magnetic shuntwith an air gap between its poles and in shunt with its armature so as to provide an additional flux to attract the armature and augment the normal increase in ull thereon as it approaches the magnet, an an electroma et acting under an abnormal current to old said member from being moved by the aforesaid electroma et.

In witness whereof, have hereunto subscribed my name in the presence of two witnesses.

THOMAS E. BARNUM.

Witnesses:

R. M. VAN Vmn'r, F. I. PARKER. 

